A world map. Mappae mundi are known to have been produced during Antiquity, but the earliest surviving example is in an Anglo-Saxon book of the early eleventh century. During the Gothic period, illuminated mappae mundi were produced for inclusion in books and as altarpieces (such as the Hereford Mappa Mundi). They functioned as visual encyclopaedias of world knowledge, incorporating material from biblical history and texts such as the Marvels of the East (concerning the mythical inhabitants of the East). In the later Middle Ages, thanks to developments in navigation and chart making, more detailed coastlines were grafted on to mappae mundi. Diagrammatic world maps, such as the T maps of Isidore of Seville, which depicted the three known continents as a T contained in a circle, were also produced during the Middle Ages.